1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel and a method for fabricating the same, wherein a fabrication process of a color filter array can be simplified.
2. Discussion of the Related Art
Liquid crystal display devices (LCDs) control light transmittance of liquid crystal cells according to a video signal to allow the liquid crystal cells to display an image corresponding to the video signal on a liquid crystal display panel arranged in the form of a matrix. In order to realize this operation, liquid crystal display devices (LCDs) include a liquid crystal display panel, where liquid crystal cells are arranged in the form of an active matrix, and driving circuits to drive the LCD panel.
Referring to FIG. 1, the liquid crystal display panel includes a upper substrate 2 where a color filter array is formed, a lower substrate 22 where a thin film transistor array 22 is formed, and a liquid crystal 11 interposed in the cell gap between the upper substrate 2 and the lower substrate 22, a lower polarizing film 21 adhered to a light-incident plane, a upper polarizing film 1 adhered to a light-emitting plane, and a compensation film 3 interposed between the lower upper substrate 2 and the upper polarizing film 1. The compensation film 3 may be further arranged between the lower polarizing film 21 and the lower substrate 22.
The color filter array includes a black matrix 4, a color filter 6, a planarizing layer 7 and an upper alignment layer 8 arranged on the upper substrate 2.
The thin film transistor array includes a thin film transistor (hereinafter, referred to simply as “TFT”), a common electrode 13, a pixel electrode 18 and a lower alignment layer 28 arranged on the lower substrate 22.
The upper substrate 2 and the lower substrate 22 are joined to each other such that the color filter array faces the thin film transistor array. The spacer 10 serves to maintain the cell gap between the two substrates.
In the color filter array, the black matrix 4 overlaps a region corresponding to the TFT of the thin film transistor array and a region corresponding to gate lines and data lines (not shown), and partitions the sub pixels. The color filter 6 is formed at each sub pixel partitioned by the black matrix 4. The sub pixel includes repeated filter patterns of R, G and B sub pixels, and may further include a W sub pixel to improve brightness. The color filter 6 includes R, G and B color filters, which render red, green and blue, respectively. When the sub pixel further includes a W sub pixel, the color filter 6 further includes a W color filter pattern at the W sub pixel. The planarizing layer 7 is formed to cover the color filter and levels out the upper substrate 2.
In the thin film transistor array, the TFT includes a gate electrode 12 connected to a gate line (not shown), a gate insulating film 24, a semiconductor pattern 14 overlapping the gate electrode 12, and a source electrode 40 in ohmic contact with the semiconductor pattern 14 and connected to the data line (not shown) that crosses the gate line, and a drain electrode 17 spaced apart from the source electrode 40 and arranged to be in ohmic contact with the semiconductor pattern 14. The TFT supplies a pixel signal through a data line to a pixel electrode 18, in response to a scanning signal through the gate line. The pixel electrode 18 is in contact with the drain electrode 17 of the TFT through a contact hole in a protective film 26. A common electrode 13 is formed in the form of a stripe such that it is alternately arranged with the pixel electrode 18. The common electrode 13 applies a common voltage which is a base voltage of liquid crystal driving.
An upper alignment film 8 and a lower alignment film 28 allow the liquid crystal 11 to be uniformly aligned.
The liquid crystal 11 rotates in accordance with an electric field generated by the common voltage supplied from the common electrode 13 and the pixel voltage supplied from the pixel electrode 18 to control light-transmittance.
An upper polarizing film 1 and a lower polarizing film 21 allow non-polarized incident lights to be linearly polarized.
Light incident to the LCD panel is linearly polarized through the lower polarizing film 21 and is transmitted to the liquid crystal 11 having refractive index anisotropy. At the same time, the light is vertically or obliquely transmitted to the liquid crystal 11. Lights that transmit the upper polarized film in respective directions have different retardation values due to the liquid crystal 11, thus causing a phase-difference. The phase-difference resulting from the transmission directions varies the properties of the transmitted lights, according to a viewing angle. The compensation film 3 offsets the optical phase-difference and thus improves viewing angle properties of the LCD panel.
FIGS. 2A and 2D are sectional views sequentially illustrating a method for fabricating the color filter array shown in FIG. 1.
An opaque resin is applied over the entire surface of an upper substrate 2 and is then patterned by photolithographic and etching processes using a first mask, to form a black matrix 4, as shown in FIG. 2A.
A red resin is deposited on the upper substrate 2 including the black matrix 4 and is then patterned by photolithographic and etching processes using a second mask, to form a red color filter pattern R, as shown in FIG. 2B. In the same manner, a green, blue, and white color filter patterns G, B and W are sequentially formed using a third, fourth, and fifth mask, respectively. Green, blue and transparent resins are used to form the green, blue, and white color filter patterns G, B and W, respectively. Although no white color filter pattern W is formed, brightness may be improved. Unless there is any white color filter pattern W, the planarizing layer 7 cannot offset the step between W sub pixels. Accordingly, it is preferable to form the white color filter pattern W, in terms of efficient planarization of the upper substrate 1, where the color filter 6 is formed.
An organic material is deposited over the entire surface of the upper surface 2 including the color filter 6 to form a planarizing layer 7, as shown in FIG. 2C. The planarizing layer 7 eliminates the topology of the sub pixels which is caused by the black matrix 2 composed of an opaque resin.
A spacer material is applied over the entire surface of the planarizing layer 7 and is then patterned by photolithographic and etching processes using a sixth mask, to form a spacer 10, as shown in FIG. 2D.
As such, at least six mask processes are required for the fabrication of the color filter array. Each of the mask processes includes a photolithographic process, which is a photographic process including a series of the steps of involving applying, exposing and developing a photoresist. The photolithographic process requires long process times and high equipment costs.
The upper substrate 1 including the thin film transistor array is joined to the lower substrate 21 including the color filter array, the liquid crystal 11 is interposed in the cell gap, and a compensation film 3 and polarized films 1 and 2 are adhered. The compensation film 3 improves display quality of the LCD panel, but has the disadvantage of causing increases in material costs and fabrication process time.